1. Field of Application
The present invention relates to an electric power converter having a plurality of semiconductor modules arrayed in successive layers, each semiconductor module having an internal semiconductor element and two power terminals.
2. Background Technology
Types of electric power converter are known, for converting between DC power and AC power, based on a stacked-layer unit having a plurality of successive layers of semiconductor modules, each semiconductor module incorporating an internal semiconductor element and two power terminals, and a plurality of cooling tubes arranged in layers corresponding to those of the semiconductor modules, for cooling the semiconductor modules. An example of such an electric power converter is described in Japanese patent publication No. 2011-135737, referred to in the following as reference D1.
FIG. 9 is a plan view illustrating the electric power converter of reference D1, and FIG. 8 is a corresponding plan view with a positive-polarity busbar 93a and negative-polarity busbar 93b removed. As shown in FIG. 9, the electric power converter 9 incorporates a stacked-layer unit 910 having alternating layers of cooling tubes 911 and semiconductor modules 92, held within a rectangular frame 96, with the semiconductor modules 92 each having a pair of power terminals collectively designated by numeral 921. The power terminals of each semiconductor module 92 consist of an AC terminal 921c (for supplying AC power to a load) and either a positive-polarity power terminal 921a or a negative-polarity power terminal 921b (for connection to the positive-polarity or negative-polarity side of a DC power source, respectively). The semiconductor modules 92 are arranged in successive layers each containing two semiconductor modules, thereby forming two columns of semiconductor modules each extending along the x-direction (i.e., the stacking direction). In each layer, the positive-polarity power terminal 921a of one semiconductor module 92 is connected to the positive-polarity busbar 93a, the negative-polarity power terminal 921b of the other semiconductor module 92 is connected to the negative-polarity busbar 93b, and the two AC power terminals 921c of that layer are connected in common to a corresponding one of a set of three AC busbars 94.
Respective end portions of the AC busbars 940 constitute external connection terminals 940, which are mounted on a terminal strip 95, for connecting to an external apparatus such as a 3-phase AC motor (not shown in the drawings). Two terminals 950 of a smoothing capacitor (not shown in the drawings) are also mounted on the terminal strip 95, with the external connection terminals 940 and capacitor terminals 950 arrayed in a single column along the x-direction as shown.
The terminal strip 95 is positioned adjacent to one side of the frame 96 (with respect to the y-direction, i.e., width direction), oriented along the x-direction. Due to the column of terminals which are mounted on the terminal strip 95 and the necessary spacings between these, the length of the terminal strip 95 along the x-direction must be made relatively large. However since the semiconductor modules 92 are arranged in two columns, the stacked-layer unit 910 is relatively short as measured along the x-direction, so that the length L1 of the frame 96 is relatively small. Thus there is a mismatch between the length L2 of the terminal strip 95 and the length L1 of the frame 96. This results in a dead space (unoccupied space) S shown in FIG. 9, which is a hindrance to minimizing the overall size of the electric power converter 9.
In addition with such a configuration, the AC busbars must be formed with respectively different shapes. This is a hindrance to reducing the manufacturing costs of the electric power converter 9 by minimizing the number of different component parts. In addition, since each AC busbar must reach both of the AC power terminals 921c in the corresponding layer of semiconductor modules 92, the AC busbars are substantially elongated. Furthermore if the overall (y-direction) width of the electric power converter 9 is minimized as far as possible, the AC busbars become spaced closely together. Hence, at least a part of each AC busbar must be made substantially narrow, to prevent contact between adjacent busbars. Such an elongated narrow shape of the AC busbars is disadvantageous from the aspects of increased electrical resistance and difficulty of forming the AC busbars (e.g., from sheet metal).